Power-assisted master cylinder



. 8- 1954 E. R. PRICE 2,685,172

' POWER-ASSISTED MASTER CYLINDER Original Filed Aug. 17, 1949 2Sheets-Sheet 1 IN VEN TOR. B {74/91 A? P/P/CE Aug., 3, 1954 2Sheets-Sheet, 2

v IN VEN TOR. 54% 162 89/ 25 BY Patented Aug. 3, 1954 UNITED STATESPATENT OFFICE POWER-ASSISTED MASTER- CYLINDER Earl R. Price, South-Bend,Ind., assignor to Bendix Aviation Corporation, South Bend, Ind acorporation of Delaware Continuation of application Serial No, 110,816,

Aug. 17, 194

Serial No. 366,540

9. This application July 7, 1953,

19 alarmsv (Cl. ll-54.6)

More specifically, the invention relates to a pressure producing devicecomprising a master cylinder, a power cylinder, and two co-axialplunger, or piston, members adapted to concurrently displace liquid fromthe master cylinder, one of said members being moved by the powercylinderpiston, and the other Of said members being moved by the forceexerted by the operator. Sorensen Patent No. 2,006,487 discloses apressure producing device of the type described in the precedingsentence.

The primary object of the present invention is to provide a device ofthis type which is appreciably improved, from the standpoint ofcommercial acceptability, over any similar devices heretofore proposed,owing to the following advantages:

(a) Improved operation because of a smoother and better feeling pressurestroke;

(1)) Improved operation because of more positive sealing of the liquidin the hydraulic system and more eflicient liquid compensation duringthe return stroke;

(0) A shorter unit for any given output requirement, reducing the spaceneeded for installation;

(d) A unit better adapted for actuation by a treadle, when the latter issubstituted for the conventional pedal; and

(e) A unit which is relatively inexpensive to manufacture, particularlywhen its operating advantages are taken into account.

A specific feature of the present invention is the provision of apower-assisted master cylinder unit having a liquid-displacing member inthe hydraulic cylinder which is of smaller effective diameter than thecylinder bore and which carries a projection adapted to control theseating and unseating of a valve associated with a port between thecylinder bore and a hydraulic, reservoir. With this arrangement, certainadvantages are realized: (a) the complete unit is shorter and thereforeeasier to locate than it would be with a conventional master cylinderpiston and sealing cup: and (b) the larger diameter of the cylinderbore, for a given displacement rating andlength of stroke, avoids theproblems which result from trying to utilize a seal and a check valve intoo small a bore.

Other objects and advantages of the present invention will becomeapparent during the fol-. lowing description of an illustrativeembodiment of the: invention, reference being had therein. to,

the accompanying drawings. in which:

Figure 1 is a diagrammatic showing of a brake operating system whichincorporates my improved pressure producing device;

Figure 2 is a longitudinal section taken through the pressure producingdevice of Figure 1;

FigureB is a closeup of part of the section shownin Figure 2;

Figure 4 is an. enlarged side view of part of the mechanism shown-inFigure 2 and Figure 5 is a section on the line 55 of Figure 4.

Referring to the drawings, my: improved liquid pressure producing devicecomprises a power cylinder I2 and. a hydraulic cylinder 14 mounted onone end of the power cylinder." The end of the hydraulic cylinder remotefrom the power cylinder has a discharge port [6 which is connected byone or more conduits 18 to one ormore hydraulically actuated motors 20,which may be used to operate wheel brakes 22,

Inside hydraulic cylinder I4 isa pressure chamber 25-, wherein theoperating pressure for motors 20 is developed jointly by theforceexerted by power cylinder piston 26 and the force exerted by theoperator on treadle 28. The lower end of the treadle is pivotallysupported at 30, andthe upper end of the treadle is pivotally connected,by means of pin 32, to a clevis 34= formed on one end of a thrust rod36.

Power cylinder I2 is preferably a differential air pressure powercylinder, utilizing either vacuum or compressed airto providethenecessary pressure differential. In ordinary automobileinstallations, a vacuum power cylinder is preferable to a compressed airpower cylinder, because the conventional intake manifold, such as theone shown diagrammatically at 38-in1' igure 1, may be used as the vacuumsource.

The vacuum power cylinder in the illustrated embodiment of the inventionis atmospheresuspended, i. e. air at atmospheric pressure is on bothsides of piston 2-6 when the mechanism is in released position. Althougha vacuumsuspended power cylinder may be used if desired; there arecertain advantages accruing from the use of an atmosphere-suspendedpower cylinder. For one thing, chamber 39 ofthe power 3 cylinder doesnot have to be sealed, since it is kept under atmospheric pressure. Thismeans that the angular movement of control rod 36 during the pressurestroke does not create any structural problem in the design of the powercylinder. Furthermore, operation of an atmosphere-suspended powercylinder is inherently smoother and less sensitive than the operation ofa vacuum-suspended power cylinder. On the other hand, speed ofoperation, which is the primary advantage of the vacuum-suspended powercylinder, is not considered as vital in installations where my improvedpressure-producing device is likely to be used, as it would be inheavier duty installations.

A closure member 48 is located between pressure chamber 24 and theinterior of power cylinder I2. The closure member may be constituted bya tubular plug screwed into the end of the hydraulic cylinder, as shown.Power cylinder piston 28, which is referred to in the claims as apressure-responsive movable wall, forms one side of control chamber 42in the power cylinder, and has a central opening 44 which permits theoperator-controlled force-transmitting member to extend into hydraulicpressure chamber 24. A hollow pressure-transmitting member 46 has atubular portion 48 which is secured at one end to power piston 28 inalignment with the opening in the piston, and which extends at the otherend through the closure member 48 into hydraulic pressure chamber 24. Inthe illustrated version of the device, the plates which constitutepiston 26 are clamped between a sleeve 58 carried by tubular member 48and a washer 52 which is held in position by a C-shaped spring lockingmember 54. Sleeve 58 is retained in position by a flange 56 on tubularmember 48. A port 58 provided in sleeve 58 is connected by means of ametal tube 58, and a coiled, flexible vacuum hose 88 to a metal tube 82which extends through an opening in the power cylinder casing, and whichis connected to manifold 38. As shown, sleeve 58 may be used as a spacerwhich determines the released position of piston 28 by engagement with aclosure plate 64 secured to the end of the power cylinder casing. Aspring 68, seated against end wall 68 of the power cylinder, returnspower cylinder piston 26 to retracted position.

An annular sealing member I8, substantially U-shaped in cross-section,is seated against the inner end of closure member 48. The inner lip 12of sealing member 18 engages the cylindrical outer surface of tubularmember 48, and the outer lip T4 of sealing member 18 engages the wall ofhydraulic pressure chamber 24, for the purpose of preventing escape ofliquid from said chamber.

Reciprocably mounted inside tubular member 48 is a plunger member 82which has one end in engagement with a sliding valve control member 84,and the other end 86 extending into hydraulic pressure chamber 24, forthe purpose of assisting power operated member 46 in displacing liquidunder pressure from the hydraulic cylinder, and also for the purpose ofgiving the operator a direct indication of, and control over, the brakeoperating pressure developed in chamber 24. Although plunger member 82and valve member 84 are preferably formed separately, as shown, forconvenience in manufacturing the device, they may be considered toconstitute jointly a plunger member, or force-transmitting member, whichprovides a thrust connection between rod 36 and the liquid in chamber24.

As shown, valve member 84 is a cylindrical, sliding valve, the exteriorof which has two reduced diameter portions providing chambers 88 and 98,which are separated by an annular land 92. Chamber 88 communicatesthrough ports 84 in tubular member 48 and port 58 in sleeve 58 with thevacuum source. Chamber 98 communicates through ports 86, passage 98 invalve member 84, and ports I88, formed in an end fitting IGI, with theatmosphere. Chamber 39 may be connected through conduit I82 to an aircleaner I84. One or more ports I86 in tubular member 48 providecommunication between the interior of the tubular member and powercylinder chamber 42. In the released, or retracted position of thedevice, ports I06 open into atmosphere chamber 98, thus permitting airat atmospheric pressure to enter chamber 42. The end of valve member 84remote from plunger member 82 is provided with a spherical socket I88which receives the ball-shaped end H8 of rod 88. The ball and socketconnection permits swiveling movement of the rod relative to the valvemember during the pressure stroke.

Use of the sliding control valve 84, instead of valve elements whichmove to and away from seated position, results in smoother operation ofthe device. Another element which contributes to improved control of thebrake actuating device is the movement-opposing member, or wave washer II2, an enlarged view of which is shown in Figure 4. Wave washer H2 ismounted between fiange 5B of tubular member 48 and flange M4 on theadjacent end of fitting II. The design of washer I I2 is such thatflange I I4 engages surfaces I I6 after land 92 has moved beyond portI86 a predetermined distance. When flange II4 engages surface H8 of thewave washer, resistance to further opening of the valve is increased,with the result that the tendency to over-shoot and cause hunting of thevalve is largely overcome. If a wider valve opening is desired, it canbe obtained by exerting sufficient force on wave washer II2 to compressthe washer axially.

The end of tubular member 48 inside the hydraulic cylinder carries anenlarged head portion I28, which may be formed as an integral part ofthe tubular member, or which may, as shown, be an annular member havinga sleeve I2I in threaded engagement with the end of the tubular member.The radially inner surface of head portion I28 engages the outer surfaceof the end portion 86 of plunger member 82. A flexible diaphragm I22 isperipherally secured to the outer portion of head I28, and covers theend of plunger member 82 to act as a seal between the hydraulic pressurechamber and the interior of tubular member 48. One of the chief reasonsfor providing the enlarged head I28 on the end of tubular member 48 isto allow use of a diaphragm which has a sufliciently large diameter topermit its periphery to be satisfactorily secured in place. In order tohold the outer edge of diaphragm I22 in position, an annular retainingmember I24 is held against one side of the diaphragm by a peenedoverbead I26 formed in head I28. The other side of diaphragm I22 liesagainst surface I28 of head I28.

A hydraulic reservoir I38 is mounted above the hydraulic cylinder, andhas a compensating port I32 which opens into hydraulic pressure chamber24. A valve element I34 is arranged when seated to prevent flow ofliquid from the hydraulic pressure chamber to the reservoir, but topermit flow in the opposite direction if a vacuunr sesame stroke. Valveelement I314! is carried. by a valve stem I36 oneend or which extendsthrough coma pensating port 532. A spring I38, supported on plug I40,in. which the compensating port. is formed, acts against a collar I42carried by valve stem I36.to urge the valve. element toward seatedposition. The lower I44 ot valve stem. I36 extends into the path. ofhead I23. of tubular member 48. During the final portion, of theretractile stroke. of tubular member 48,. head por-. tion IL2hengagesvalve stem I44 to move the latter angularly and' thereby liftone side of valve element: I34 to establish tree, communication be,tween the; hydraulic pressure chamber and the interior of reservoir I30;

Plungermember 82 and valve control. member 84 areurged. toward; releasedposition by a compression spring I46, oneend of which engages. av

flange I48: on plunger member 82', and the other end? of which engages.the end of threaded sleeve I2I'. The particular positiorrof spring I46.is. not important, provided it. exerts a. force tending to move. valvemember 84 toward the left: with re.- spect to; tubular member 48, the.leftward portion of. which. cooperates with valve member 84 incontrolling operation of power cylinder piston 26. The released positionof valve member 84 is determined by a. substantially Uy-shaped.positioning member I52, the arms of which extend through segmentalslots. I154. provided. in sleeve 50, into. annular slot I56. in valvemember 84.. Slots I54. have a sufficiently wide axial dimension to allowthe: movement. required to actuate the control valve.

The. way in which my improved pressure-producingw device operates. isbelieved to be obvious from the foregoing description. However, thefollowing summary is given for the sakeof clarity. When the operatordepresses treadle 28, rod 36 moves valve member 84, against theresistance of spring I46, to first bring land BZinto alignment with portI06, thereby cutting off communication between power; chamber 42 and theatmosphere. Additional movement of valve member 84 toward therightcarries land 92 past port L06; establish.- ing-communicationbetween chamber 42 and the vacuum source. Evacuation of air from chamber42 causes. av pressure differential to act on power cylinder piston 26,moving it. toward. the right, againstv the resistance of return spring65.

As power cylinder piston 26' moves toward the right, it drivespressure-transmitting member 46 on itspressure stroke, displacing liquidfrom hydraulic pressure chamber 24. The initial movement of head portionI20 of pressure-transmitting member 46 disengages the lower end I44 ofvalve stem I36. Spring I38 is thus permitted to seat valve element I34,thereby preventing flow of liquid under pressure from chamber 24 to thereservoir.

The amount of liquid which isdisplaced from chamber 24. to actuate themotors 20 during a given length of pressure stroke depends upon theouter diameter of tubular member 48. In normal operation of the device,the work done by the power cylinder piston is responsible for displacingan amount of liquid proportional to the annular area between the outersurface of tubular member 48. and the inner surface of head portion I20which engages plunger member 82; the work done by the operator isresponsible for displacing an amount of liquid proportional to the areaof the end portion 86 of plunger member 82. Except ion the lost motionrequired to operate the valve,

force.

tubular member 48- and plunger member 82 move as a unit during thepressure stroke.

The amount of pressure-developed in the brake system is indicated tothe. operator by the direct reaction of the liquidchamber 24- againstthe end or plunger memberBZ. Therefore, in order toincrease the brakeapplyingpressure, the opera.

tor must increase the force which he exerts onthe treadle. Furthermore;in order to continue the brake-applying stroke of power cylinder piston26, the operator must continue to move valve member 84 toward the right.When valvemember 84 ceases to move toward the right, the follow-upmovement of power piston 26 and tubular member 48: brings ports I06 intoalignment with land: 92, thus placing the valve in lapped posi tion,which position will be retained untit valve member 84 is moved eithertoward the left tore lease the brakes, or toward the right to furtherapply the brakes.

- of valve member 84 engages wave washer I.I2,

tending toprevent. an excessive valve opening movement. If the operatordesires to obtain a maximum valve opening movement he; can com.- presswave washer N 2 with additional applying- However, the presence of theWave washer tends to avoid the fluttering, or hunting ac-. tion of thevalve which: can occur when the valve opening movement is. unrestricted.If the power cylinder should fail tobe effective, the force. exerted bythe operator will flatten the wave washer between the end of valvemember 34; and the flange. 56 of tubular member 48, permitting theoperator to drive the entire assembly with physi-. cal force, attainingfull displacementofliquid: in the hydraulic system.

When pressure on treadle 28. is removed, spring I46. moves valve member84 back to the position in which chamber 42 isin communication with theatmosphere. As air enters chamber 42', the pressure differential overpower piston 26 is reduced, and eventually destroyed, permitting spring66 to. return the power piston to released position. The entireliquid-displacing unitis thuswithdrawn to the left in hydraulic pressurechamber 24', releasing the brake-applying pressure.

During the return stroke, a predetermined pressure is maintained in thehydraulic lines by means of the conventional residual pressure checkvalve I58. For a description of check valve I58, reference may be had toBowen Patent No. 1,841,354. If the pressure in chamber 24 falls belowatmospheric pressure during the return stroke, valve element I34 will beunseated by the pressure of liquid in the reservoir, which willthen flowinto chamber 24 to keep the chamber filled. When the head I20 ofpressure-transmitting member 46 reaches the end of itsretractile-strokeit engagesvalve stem: I35 to lift one side of valve element I34, therebyre-establishingfree comsignificant safety feature, because the timerequired to bring the operators foot into engagement with the brakecontrol member is one of the important time delays in obtaining brakeapplication. Furthermore, in automobiles which no longer have a clutchpedal in the drivers compartment, it is particularly desirable to use abrake-operating treadle which is similar to the accelerator treadle. Theappearance of the operators compartment is improved and the foot room isincreased.

Utilization of a brake control treadle places the following limitationson design of the master cylinder. In the first place, the mastercylinder stroke has to be longer than in the case of the conventionalbrake pedal, because the treadle acts directly on the master cylinder,without the conventional lever arm movement ratio. Furthermore, becausethe operator does not have a mechanical advantage in operating themaster cylinder, the initial frictional forces must be reduced to aminimum, if satisfactory treadle feel is to be obtained.

Sealing diaphragm I22 is preferred to the conventional sliding seal bothbecause it reduces the frictional opposition to movements of plungermember 82 and valve member 84, and because it provides a positive sealwhich insures against admission of liquid to the interior of tubularmember 48. Use of diaphragm I22 necessitates the provision of anenlarged head I20 on the end of pressure-transmitting member 46. It isdifiicult, if not impossible, to satisfactorily secure a diaphragmsealing member in position if its diameter is extremely small. On theother hand, it is not feasible to enlarge the working diameter oftubular member 48 because such a change would necessitate making theoperating stroke of the master cylinder too short for satisfactorycontrol.

Because of the use of the enlarged head I20 on pressure-transmittingmember 46, a fixed annular seal, such as the seal I0, is required at theend of the hydraulic cylinder adjacent the power cylinder. Use of thefixed, i. e. stationary, seal ID has th additional advantage ofpermitting the hydraulic cylinder to be shorter than it would be if aconventional piston having spaced lands were used.

The enlarged head I20 on pressure-transmitting member 46 provides aconvenient flange for engaging the stem of valve member I34 to tilt thevalve in the released position of the device. Use of the seating valveI34, rather than the conventional uncovered port, together with use ofthe stationary annular seal I0, avoids the need for machining the boreof the hydraulic cylinder. Use of the seating valve I34 also simplifiesconstruction of the head portion I20 of pressuretransmitting member 46,inasmuch as the head does not need to carry a seal engaging the wall ofchamber 24.

Although a particular embodiment of my invention has been described, itwill be understood by those skilled in the art that the object of theinvention may be attained by the use of constructions different incertain respects from that disclosed without departing from theunderlying principles of the invention.

I claim:

1. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a differential air pressurepower cylinder, a hydraulic cylinder mounted on one end of the powercylinder and having a pressure chamber provided with a discharge port, apressure-responsive movable wall in the power cylinder having a centralopening, a tubular pressure-transmitting member secured at one end tothe movable wall in alignment with said opening and extending at theother end into the hydraulic pressure chamber, said tubular memberhaving a port which is adapted, to provide communication between theinterior of the tubular member and the power cylinder chamber formedbetween the movable wall and the end of the power cylinder adjacent thehydraulic cylinder, a cylindrical valve member slidably mounted insidethe tubular member, the exterior of the valve member having tworeduced-diameter portions providing chambers which are separated by anannular land and which are in communication, respectively, with theatmosphere and with a vacuum source, the atmosphere-connected valvechamber being in communication with the port in the tubular member inreleased position, an operator operated rod connected to the end of thevalve member, the power cylinder chamber through which the rod and valvemember extend being open to the atmosphere, a plunger member movableinside the tubular member and having one end in engagement with thevalve member and the other end extending into the hydraulic pressurechamber, an annular head on the end of the tubular member inside thehydraulic pressure chamber, said head having an outer portion of greaterdiameter than the tubular member, a flexible diaphragm peripherallysecured to the outer portion of the head and covering the end of theplunger member to act as a seal between the hydraulic pressure chamberand the interior of the tubular member, a spring which urges the valvemember toward released position, a hydraulic reservoir mounted above thehydraulic cylinder and having a port which opens into the hydraulicpressure chamber, a valve element arranged when seated to prevent flowof liquid from the hydraulic pressure chamber to the reservoir, a springtending to seat the valve element, and a valve stem associated with thevalve element and extending into the path of the head on the tubularmember, said stem being moved angularly by engagement with the headduring the final portion of its retractile stroke to unseat the valveelement and thereby permit communication between the hydraulic pressurechamber and the reservoir.

2. A liquid pressure producing device, in which physical force issupplemented by power assistance, comprising a differential air pressurepower cylinder, a hydraulic cylinder mounted on one end of the powercylinder and having a pressure chamber provided with a discharge port, apressure-responsive movable wall in the power cylinder having a centralopening, a tubular pressure-transmitting member secured at one end tothe movable wall in alignment with said opening and extending at theother end into the hydraulic pressure chamber, said tubular memberhaving a port adapted to provid communication between the interior ofthe tubular member and the power cylinder chamber formed between themovable wall and the end of the power cylinder adjacent the hydrauliccylinder, a cylindrical valve member slidably mounted inside the tubularmember, the exterior of the valve member having reduceddiameter portionsproviding two chambers which are in communication, respectively, withthe atmosphere and with a vacuum source, the atmosphere-connected valvechamber being in communication with the port in the tubular member inreleased position, an operator operated rod connected to the end of thevalve member, th power cylinder chamber through which the rod and valvemember extend being open to the atmosphere, a plunger member locatedinside the tubular member and arranged to move with the valve member,one end of the plunger member extending into the hydraulic pressurechamber, an annular head on the end of the tubular member inside thehydraulic pressure chamber, said head having an outer portion of greaterdiameter than the tubular member, a flexible diaphragm peripherallysecured to the outer portion of the head and covering the end of theplunger member to act as a seal between the hydraulic pressur chamberand the interior of the tubular member, a spring which urges the valvemember toward released position, a hydraulic reservoir mounted above thehydraulic cylinder and having a port which opens into the hydraulicpressure chamber, a valve element arranged when seated to prevent flowof liquid from the hydraulic pressure chamber to the reservoir, a springwhich tends to seat the valve element, and a valve stem associated withthe valve element, said stem being moved angularly by the head on thetubular member during the final portion of its retractile stroke toestablish communication between the hydraulic pressure chamber and thereservoir.

3. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a differential air pressurepower cylinder, a hydraulic cylinder mounted on one end of the powercylinder and having a pressure chamber provided with a discharge port, apressure-responsive movable wall in the power cylinder having a centralopening, a tubular pressure-transmitting member secured at one end tothe movable wall in alignment with said opening and extending at theother end into the hydraulic pressure chamber, said tubular memberhaving a port which is adapted to provide communication between theinterior of the tubular member and the power cylinder chamber formedbetween the movable wall and the end of the power cylinder adjacent thehydraulic cylinder, a valve control member movable inside the tubularmember and arranged to selectively connect the port in the tubularmember to the atmosphere or to a vacuum source, an operator operated rodconnected to one end of the valve control member, the power cylinderchamber through which the rod and valve control member extend being opento the atmosphere, a plunger member located inside the tubular memberand arranged to move with the valve control member, one end of theplunger member extending into the hydraulic pressure chamber, thetubular member and the plunger member having a combined effectiveliquid-displacing area in the pressure chamber smaller than thecross-sectional area of said pressure chamber, an annular head on theend of the tubular member inside the hydraulic pressure chamber, saidhead having an outer portion of greater diameter than the tubularmember, a flexible diaphragm peripherally secured to the outer portionof the head and covering the end of the plunger member to act as a sealbetween the hydraulic pressure chamber and the interior of the tubularmember, a hydraulic reservoir mounted above the hydraulic cylinder andhaving a port which opens into the hydraulic pressure chamber, a valveelement arranged when seated to prevent flow of liquid from thehydraulic pressure chamber to the reservoir, a spring which tends toseat the valve element, and a valve stem associated with the valveelement, said stem being moved angularly by the head on the tubularmember during the final portion of its retractile stroke to establishcommunication between the hydraulic pressure chamber and the reservoir.

4. A liquid pressure producing device, in which physical force issupplemented by power assistance, comprising a differential air pressurepower cylinder, a hydraulic cylinder mounted on one end of the powercylinder and having a pressure chamber provided with a discharge port, apressure-responsive movable wall in the power cylinder having a centralopening, said movable wall dividing the power cylinder into a constantpressure chamber and a control chamber, a tubular pressure-transmittingmember secured at one end to the movable wall in alignment with saidopening and extending at the other end into the hydraulic pressurechamber, said tubular member having a port adapted to providecommunication between the interior of the tubular member and the controlchamber of the power cylinder, a valve control member movable inside thetubular member and arranged to selectively connect the port in thetubular member to the atmosphere or to a vacuum source, an operatoroperated rod connected to the one end of the valve control member, aplunger member located inside the tubular member and arranged to movewith the valve control member, one end of the plunger member extendinginto the hydraulic pressure chamber, the tubular member and the plungermember having a combined effective liquid-displacing area in thepressure chamber smaller than the cross-sectional area of said pressurechamber, an annular head on the end of the tubular member inside thehydraulic pressure chamber, a flexible diaphragm peripherally secured tothe head and covering the end of the plunger member to act as a sealbetween the hydraulic pressure chamber and the interior of the tubularmember, a hydraulic reservoir mounted above the hydraulic cylinder andhaving a port which opens into the hydraulic pressure chamber, a valveelement arranged when seated to prevent flow of liquid from thehydraulic pressure chamber to the reservoir, a spring tending to seatthe valve element, and a valve stem associated with the valve element,said stem being moved angularly by the head on the tubular member duringthe final portion of its retractile stroke to establish communicationbetween the hydraulic pressure chamber and the reservoir.

5. A liquid pressure producing device, in which physical force issupplemented by power assistance, comprising a power cylinder, ahydraulic cylinder mounted on one end of the power cylinder and having apressure chamber, a pressureresponsive movable wall in the powercylinder, a tubular pressure-transmitting member connected to themovable wall and provided with an enlarged head member located in thehydraulic pressure chamber, an operator operated plunger memberreciprocably mounted in the pressuretransmitting member for controllingoperation of the power cylinder by means of its movements with respectto the pressure-transmitting member, one end of the plunger member beingsubjected to the pressure in the hydraulic pressure chamber, thepressure-transmitting member and the plunger member having a combinedeffective liquid-displacing area in the pressure chamber smaller thanthe cross-sectional area of said pressure chamber, a flexible diaphragmperipherally secured to the enlarged head member and covering the end ofthe plunger member to act as a seal between the hydraulic pressurechamber and the interior of the pressure-transmitting member, ahydraulic reservoir mounted above the hydraulic cylinder and having aport which opens into the hydraulic pressure chamber, a valve elementarranged when seated to prevent flow of liquid from the hydraulicpressure chamber to the reservoir, a spring tending to seat the valveelement, and a valve stem associated with the valve element, said stembeing moved angularly by the head member during the final portion of itsretractile stroke to establish communication between the hydraulicpressure chamber and the reservoir.

6. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a power cylinder, ahydraulic cylinder located at one end of the power cylinder and having apressure chamber, a pressureresponsive movable wall in the powercylinder,

a hollow pressure-transmitting member connected to the movable wall andextending into the hydraulic pressure chamber, a sealing member engagingthe outer surface of said pressuretransmitting member to prevent escapeof liquid from the hydraulic pressure chamber, an operator operatedplunger member which is reciprocably mounted in thepressure-transmitting member and which controls operation of the powercylinder by means of its movements with respect to thepressure-transmitting member, one end of the plunger member beingsubjected to the pressure in the hydraulic pressure chamber, thepressure-transmitting member and the plunger member having a combinedeffective liquid-displacing area in the pressure chamber smaller thanthe cross-sectional area of said pressure chamber, a flexible diaphragmsecured to the pressure-transmitting member and covering the end of theplunger member to act as a seal between the hydraulic pressure chamberand the interior of the pressure-transmitting member, a hydraulicreservoir having a port which opens intothe hydraulic pressure chamber,and a valve element which is arranged when seated to prevent flow ofliquid from the hydraulic pressure chamber to the reservoir and which isheld open by the pressure-transmitting member when the latter is inretracted position.

7. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a power cylinder, ahydraulic cylinder located at one end of the power cylinder and having apressure chamber, a pressureresponsive movable wall in the powercylinder, a hollow pressure-transmitting member connected to the movablewall and extending into the hydraulic pressure chamber, an operatoroperated plunger member which is reciprocably mounted in thepressure-transmitting member and which controls operation of the powercylinder by means of its movements with respect to thepressuretransmittin member, one end of the plunger member beingsubjected to the pressure in the hydraulic pressure chamber, thepressure-transmitting member and the plunger member having a combinedeflfective liquid-displacing area in the pressure chamber smaller thanthe crosssectional area of said pressure chamber, a flexible diaphragmwhich is secured to the pressure-transmitting member and which acts as aseal between the hydraulic pressure chamber and the interior of thepressure-transmitting member, a hydraulic reservoir having a port whichopens into the hydraulic pressure chamber, and a valve element which isarranged when seated to prevent flow of liquid from the hydraulicpressure chamber to the reservoir and which is held open by thepressure-transmitting member when the latter is in retracted position.

8. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a power cylinder, ahydraulic cylinder located at one end of the power cylinder and having apressure chamber, a closure member between said pressure chamber and theinterior of the power cylinder and provided with an openingtherethrough, a pressure-responsive movable wall in the power cylinder,a hollow pressure-transmitting member connected to the movable wall andextending through the opening in the closure member into the hydraulicpressure chamber, an annular sealing member seated against said closuremember and engaging the outer surface of said pressure-transmittingmember to prevent escape of liquid from the hydraulic pressure chamber,an operator operated plunger member which is reciprocably mounted in thepressure-transmitting member and which controls operation of the powercylinder by means of its movements with respect to thepressuretransmitting member, the end of the plunger member adjacent thehydraulic pressure chamber being subjected to the pressure in saidchamber, the pressure-transmitting member and the plunger member havinga combined effective liquid-displacing area in the pressure chamberequal to the area of the opening in the closure member, and a flexiblediaphragm which is secured to the pressure-transmitting member and whichacts as a seal between the hydraulic pressure chamber and the interiorof the pressuretransmitting member.

9. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a power cylinder, ahydraulic cylinder located at one end of the power cylinder and having apressure chamber, a closure member between said pressure chamber and theinterior of the power cylinder and having an opening therethrough, apressure-responsive movable wall in the power-cylinder, a hollowpressuretransmitting member connected to the movable wall and extendingthrough the opening in the closure member into the hydraulic pressurechamber, an annular sealing member coacting with said closure member toprevent escape of liquid from the hydraulic pressure chamber, anoperator operated plunger member which is reciprocably mounted in thepressure-transmitting member and which controls operation of the powercylinder by means of its movements with respect to thepressure-transmitting member, the end of the plunger member adjacent thehydraulic pressure chamber being subjected to the pressure in saidchamber, the pressure-transmitting member and the plunger member havinga combined effective liquid-displacing area in the pressure chamberequal to the area of the opening in the closure member, a hydraulicreservoir having a port which opens into the hydraulic pressure chamber,and a valve element which is arranged when seated to prevent flow ofliquid from the hydraulic pressure chamber to the reservoir and which isheld open by the pressuretransmitting member when the latter is inretracted position.

10. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a power cylinder, ahydraulic cylinder located at one end of the power cylinder and having apressure chamber, a closure member between said pressure chamber and theinterior of the power cylinder and having an openin therethrough, apressure-responsive movable wall in the power cylinder, a tubu larpressure-transmitting member connected to the movable wall and extendingthrough the opening in the closure member into the hydraulic pressurechamber, an annular sealing member seating against said closure memberand engaging the outer surface of said pressure-transmitting member toprevent escape of liquid from the hydraulic pressure chamber, anoperator operated plunger member which is reciprocably mounted in thepressure-transmitting member and which controls operation of the powercylinder by means of its movements withrespect to thepressure-transmitting member, the end of the plunger member adjacent thehydraulic pressure chamber being subjected to the pressure in saidchamber, the pressure transmittin member and the plunger member having acombined effective liquid-displacing area in the pressure chambersmaller than the cross-sectional area of said pressure chamber, and asealing member which prevents escape of liquid from the hydraulicpressure chamber through the pressure-transmitting member.

11. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a power cylinder, ahydraulic cylinder located at one end of the power cylinder and having apressure chamber, a pressure-responsive movable wall in the powercylinder, a hollow pressure-transmitting member connected to the movablewall and extendin into the hydraulic pressure chamber, a plunger memberwhich is reciprocably mounted in the pressuretransmitting member andwhich controls operation of the power cylinder by means of its movementswith respect to the pressure-transmitting member, the end of the plungermember adjacent the hydraulic pressure chamber being subjected to thepressure in said chamber, and a movement-opposin member mounted betweenaxially-spaced surfaces provided by the movable wall and by the plungermember, said movementopposing member being axially spaced in releasedposition from at least one of said surfaces and being axially yieldableunder pressure, said movement-opposing member acting to increase theforce opposing further movement of the plunger member with respect tothe pressure-transmitting member after a predetermined amount ofmovement of the plunger member on the applying stroke.

12. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a diflerential air pressurepower cylinder, a hydraulic cylinder located at one end of the powercylinder and having a pressure chamber, a pressure-responsivemovablewall in the power cylinder having a central opening, a tubularpressure-transmitting member secured at one end to the movable wall inalignment with said opening and extending at the other end into thehydraulic pressure chamber, said tubular member having a port adapted toprovide communication between the interior of the tubular member and thepower cylinder chamber formed between the movable wall and the end ofthe power cylinder adjacent the hydraulic cylinder, a cylindrical valvemember slidably mounted inside the tubular member, the exterior of thevalve member having two reduced-diameter portions providing chamberswhich are separated by an annular land and which are in communication,respectively, with the atmosphere and with a vacuum source, theatmosphere-connected valve chamber being in communication with the portin the tubular member in released position, and a plunger member locatedinside the tubular member and operatively connected to the valve member,one end of the plunger member being subjected to the pressure in thehydraulic pressure chamber.

13. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a diiTerential air pressurepower cylinder, a hydraulic cylinder mounted on one end of the powercylinder and having a pressure chamber which is provided with adischarge port, a pressure-responsive movable wall in the power cylinderhaving a central opening, said movable wall dividing the power cylinderinto a constant pressure chamber and a control cham-- ber, a tubularpressure-transmitting member secured at one end to the movable wall inalignment with said opening and extending at the other end into thehydraulic pressure chamber, said tubular member having a port which isadapted to provide communication between the interior of the tubularmember and the control chamber of the power cylinder, a slide valvemovable inside the tubular member and arranged to selectively connectthe port in the tubular member to the atmosphere or to a vacuum source,the interior of the valve being in constant communication with theatmosphere, a portion of the exterior of the valve being in constantcommunication with vacuum, an operator operated rod connected to the endof the valve, a plunger member located inside the tubular member andarranged to move in conformity with the valve, one end of the plungermember extending into the hydraulic pressure chamber, an annular head onthe end of the tubular member inside the hydraulic pressure chamber,said head having an outer portion of greater diameter than the effectiveliquid-displacing diameter of the tubular member and an inner portionwhich engages the outer surface of the plunger member, and a flexiblediaphragm which is peripherally secured to the outer portion of the headand which covers the end of the plunger member to act as a seal betweenthe hydraulic pressure chamber and the interior of the tubular member.

14. A liquid pressure-producing device, in which physical force issupplemented by power assistance, comprising a differential air pressurepower cylinder, a hydraulic cylinder mounted on one end of the powercylinder and having a pressure chamber provided with a discharge port, apressure-responsive movable wall in the power cylinder having a centralopening, a tubular pressure-transmitting member secured at one end tothe movable wall in alignment with said open ing and extending at theother end into the hydraulic pressure chamber, said tubular memberhaving a port adapted to provide communication between the interior ofthe tubular member and the power cylinder chamber formed between themovable wall and the end of the power cylinder adjacent the hydrauliccylinder, a slide valve movable inside the tubular pressure-transmittingmember and arranged to selectively connect the port in the latter memberto the atmosphere or to a vacuum source, an operator operated rodconnected to the end of the valve, the power cylinder chamber throughwhich the rod and valve extend and the interior of the valve being opento the atmosphere, a plunger member located inside the tubularpressure-transmitting member and arranged to move with the valve, oneend of the plunger member extending into the hydraulic pressure chamber,an annular head on the end of the tubular pressure-transmitting memberinside the hydraulic pressure chamber, said head having an outer portionof greater diameter than the effective liquid-displacing diameter of thetubular pressure-transmitting member and an inner portion which engagesthe outer surface of the plunger member, and a flexible diaphragm whichis peripherally secured to the outer portion of the head and whichcovers the end of the plunger member to act as a seal between thehydraulic pressure chamber and the interior of the tubularpressure-transmitting member, said valve being interposed between and incontact with said operator operated rod and said plunger member wherebyforce may be transmitted from either said rod or said plunger throughsaid valve to the other.

15. In a liquid pressure-producing device, an action-and-reaction-forcemeans comprising a differential air pressure power cylinder having apressure-responsive movable wall therein, a hydraulic cylinder mountedon one part of said power cylinder, a tubular pressure-transmittingmember secured to said wall and projecting into said hydraulic cylinder,valve control and reaction pressure means movable inside said tubularmember and comprising a tubular valve having its opposite endspositioned on opposite sides of said wall and a plunger which extendsfrom physical contact with one end of said tubular valve into saidhydraulic cylinder, a flexible fluid impervious diaphragm fitted overthe hydraulic cylinder ends of said tubular pressure-transmitting memberand said plunger, a manually operable rod engaged with the other end ofsaid tubular valve and operable to receive reaction thrust from saidplunger through the intermediary of said valve, said valve having itsinterior in constant communication with the atmosphere, a first port insaid tubular pressure-transmitting member, a second port in said valvecommunicable with said first port, two spaced port-severing landsprovided on the outer periphery of said valve, one of said lands beingoperable to control communication between said first and second ports,an annular chamber formed between said lands and said tubularpressure-transmitting member and said valve, and a third port in saidtubular pressure-transmitting member in constant communication with saidannular chamber and adapted to be connected to a source of vacuum, saidannular chamber being selectively connected with said first port whenthe latter is disconnected from said second port.

16. In a liquid pressure-producing device, an action and reaction forcemeans comprising a differential air pressure power cylinder having apressure-responsive movable wall therein, a hydraulic cylinder locatedat one end of the power cylinder and having a pressure chamber therein,a closure member between said pressure chamber and the interior of thepower cylinder and having an opening therethrough, a tubular-pressuretransmitting member connected to the movable wall and extending throughthe opening in the closure member into the hydraulic pressure chamber,sealing means coacting with said closure member to prevent escape ofliquid from said latter chamber, valve control and reaction pressuremeans including a valve member reciprocably mounted centrally of saidmovable wall, manual means for actuating said valve member to produce apower stroke of said movable wall, a plunger reciprocably mounted in thepressure transmitting member in substantial alignment with the valvemember for transmitting the reaction force to said manual means throughthe valve member, the end of the plunger remote from the valve memberbeing subjected to the pressure in the hydraulic pressure chamber, thepressure-transmitting member and the plunger member having a combinedeffective liquid-displacing area in the pressure chamber equal to thearea of the opening in the closure member, and sealing means forpreventing the escape of liquid from the latter chamber through thetubular pressure transmitting member.

17. A liquid pressure producing device in which physical force issupplemented by power assistance, comprising a differential air pressurepower cylinder, a hydraulic cylinder located at one end of the powercylinder and having a pressure chamber, a pressure responsive movablewall in the power cylinder having a central opening, a tubularpressure-transmitting member extending at one end into the hydraulicpressure chamber and having its opposite end secured to the movable wallin alignment with said opening, the latter end of said tubular memberbeing provided with a valve extension having a port adapted to providecommunication between the interior of the said extension and the powercylinder chamber formed between the movable Wall and the end of thepower cylinder adjacent the hydraulic cylinder, a cylindrical valvemember slidably mounted inside the valve extension of the tubularmember, the exterior of the valve member having reduced-diameterportions providing valve lands which define a pair of chambers incommunication respectively with the atmosphere and with a vacuum source,the atmosphere-connected valve chamber being in communication with theport in the valve extension when the movable wall is in releasedposition, a plunger member located inside the tubularpressure-transmitting member and adapted to transmit reaction pressurefrom the hydraulic pressure chamber to said valve member, the end of theplunger member adjacent the hydraulic chamber being subjected to thepressure in said latter chamber, and sealing means for preventing theescape of liquid from the hydraulic pressure chamber between saidplunger and said pressure transmitting member.

18. A hydraulic pressure producing device comprising a differential airpressure power cylinder, a hydraulic cylinder mounted on one end of thepower cylinder and having a pressure chamber which is provided with adischarge port, a closure member between said pressure chamber and theinterior of the power cylinder and provided with an openingtherethrough, a pressure-responsive movable wall in the power cylinder,a force-transmitting member, one end of which engages the movable walland the other end of which extends through the opening in the closuremember into the hydraulic pressure chamber, the relative effectivediameters of said hydraulic pressure chamber and that portion of theforce-transmit- 17 ting member which extends therein being such as toprovide substantial clearance therebetween, an annular sealing memberseated against said closure member and engaging the outer surface of theforce-transmitting member to prevent escape of liquid from the hydraulicpressure chamber, a hydraulic reservoir mounted above the hydrauliccylinder and having a port which opens into the hydraulic pressurechamber, a valve element which is located adjacent to the closure memberand which is arranged when seated to prevent flow of liquid from thehydraulic pressure chamber to the reservoir, a spring which tends toseat the valve element, a valve stem associated with the valve elementwhich extends into the hydraulic pressure chamber, and a valveunseatingprojection on the force-transmitting member inside the hydraulicpressure chamber which engages the valve stem during the final portionof the retractile stroke to lift one side of the valve element andthereby permit communication between the hydraulic pressure chamber andthe reservoir.

19. A hydraulic pressure device comprising a power cylinder, a hydrauliccylinder mounted on one end of the power cylinder and having a pressurechamber which is provided with a discharge port, a closure memberbetween said pressure chamber and the interior of the power cylinder andprovided with an opening therethrough, a pressure-responsive movableWall in the power cylinder, a force-transmitting member, one end ofwhich engages the movable Wall and the other end of which extendsthrough the opening in the closure member into the hydraulic pressurechamber, the relative efiective diameters of said hydraulic pressurechamber and that portion of the force-transmitting member which extendstherein being such as to provide substantial clearance therebetween, ahydraulic reservoir associated with the hydraulic cylinder and having aport which opens into the hydraulic pressure chamber, a valve elementwhich is located adjacent to the closure member and which is arrangedwhen seated to prevent flow of liquid from the hydraulic pressurechamber to the reservoir, a spring which tends to seat the valveelement, a valve stem associated with the valve element which extendsinto the hydraulic pressure chamber, and a valve-unseating projection onthe force-transmitting member inside the hydraulic pressure chamberwhich engages the valve stem during the final portion of the retractilestroke to lift one side of the valve element and thereby permitcommunication between the hydraulic pressure chamber and the reservoir.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,781,869 Bragg et al. Nov. 18, 1930 2,006,487 Sorensen July2, 1935 2,260,491 Stelzer Oct. 28, 1941 2,407,097 Porter Sept. 3, 19462,526,457 Bradbury Oct. 17, 1950 2,532,960 Stelzer Dec. 5, 19502,617,261 Ringer Nov. 11, 1952 FOREIGN PATENTS Number Country Date747,273, France Mar. 28, 1933

